1. Technical Field
The disclosure relates to an endoscope apparatus configured to be introduced into a living body to capture images inside the living body.
2. Related Art
In the related art, an endoscope apparatus is widely used for various kinds of examinations in a medical field and an industrial field. Among such endoscope apparatus, a medical endoscope apparatus is capable of capturing an in-vivo image inside a body cavity even without cutting a subject by introducing, into the body cavity of the subject such as a patient, an insertion portion provided with an image sensor including a plurality of pixels, formed in a thin long shape, and having flexibility. Therefore, there is little burden on the subject and the medical endoscope apparatus is more widely used.
As an observation method of such an endoscope apparatus, a white light imaging (WLI) method using white illumination light; and a narrow band imaging (NBI) method using illumination light formed of two kinds of narrow-band light respectively included in blue and green wavelength bands (narrow-band illumination light) are already known. Among these, the narrow band imaging method is capable of obtaining an image in which capillary vessels, microscopic patterns of a mucosa, and the like existing in a mucous membrane surface layer of the living body can be displayed in a highlighted manner. According to the narrow band imaging method, a lesion site in the mucous membrane surface layer of the living body can be more accurately discovered. As for such observation methods in the endoscope apparatus, there is a demand to achieve observation by switching between the white light imaging method and the narrow band imaging method.
A light receiving surface of an image sensor, in which an image is to be captured by a single-plate image sensor, is provided a color filter in order to generate and display a color image by the above-described observation methods. In the color filter, filters that pass light of red (R), green (G), green (G), and blue (B) wavelength bands are arrayed as one filter unit (unit) per pixel, and the array is generally so-called Bayer array. In this case, each pixel receives light of a wavelength band having passed through the filter, and the image sensor generates an electric signal of a color component corresponding to the light of the wavelength band. Therefore, interpolation processing to interpolate a signal value of a color component that has not passed through the filter and is missing is performed in each pixel in processing to generate a color image. Such interpolation processing is called demosaicing processing (refer to Japanese Laid-open Patent Publication No. 8-237672, for example).
Electric signals generated by an image sensor provided with the color filter may have different gain between color components due to differences in transmission characteristics of the filters and the like. Therefore, the gain of the electric signals of the respective color components are adjusted between the color components at the time of generating a color image signal based on the electric signals of the respective color components of red, green, and blue. A color image expressing colors of the subject can be obtained by generating the color image signal by applying the demosaicing processing using the electric signals having the gain adjusted.